The present invention relates to shield apparatus for driving tunnels, galleries or similar excavations; and more particularly, to drive members or poling plates therefor.
It is known to construct shield apparatus from a plurality of poling plates or drive members arranged side-by-side forming a shield supported and guided on a frame. The drive members contact the tunnel wall being produced and are advanced individually or in groups in the driving direction by means of rams connected between the drive members and the support frame. It is also known to make the individual drive members from pivotably-interconnected front and rear parts. Such a construction is described in German Pat. Specification No. 2,555,524. The pivotal connections between the front and rear parts or components of the drive members impart a certain flexibility to the shield and permit the shield to adapt to deviations in the tunnel path. This is particularly useful where the tunnel takes a slightly curvilinear course since the tunnel wall can then exert extreme forces on the drive member, especially the rear regions thereof.
Although shield apparatus employing such pivotable drive members has performed well, the one drawback of this design is that the pivot connection and the front and rear components of each drive member needs to be constructed within close tolerances to ensure that the outer surfaces of the components, which define and support a region of the tunnel wall, can be aligned with one another. If such alignment is not achieved, one or other of the components may not quite contact the tunnel wall and the other component will then encounter greater driving resistance and loading. Furthermore, settlements can be caused over the unsupported tunnel wall region. Naturally, the fabrication of drive member components, usually from sheet steel, and the pivot connections within close tolerances considerably increases the overall cost of the shield apparatus.
An object of the present invention is to provide an improved drive member and shield apparatus.